Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, and a non-transitory computer readable storage medium.
Description of the Related Art
In an image capturing apparatus such as a digital camera, when shooting a video or when displaying a live viewing image, it is desirable to reduce the size of pixels in an image signal and perform development processing as early as possible in the processing. The object is to reduce the scale of the development circuit and to suppress power consumption to a low level. The reduction processing at this time can be performed during readout by summing/thinning out pixels on an image sensor, or otherwise subsequently with the development circuit. Also, in the case in which the image size for video recording in full HD, QFHD or the like is different from the pixel size read out from the image sensor, enlargement or reduction of the size of pixels in the image signal is performed within the circuit, for example.
A decrease in image quality is brought about if reduction is performed using simple linear interpolation, for example, in order to reduce the image signal. In contrast, in Japanese Patent Laid-Open No. 2009-135598 and Japanese Patent Laid-Open No. 2006-67214, a reduced image that has retained its sharpness is generated by determining the direction of change between pixels and performing interpolation on the thinned out pixels.
However, no method of interpolating pixels according to a reduction rate is described in Japanese Patent Laid-Open No. 2009-135598 or Japanese Patent Laid-Open No. 2006-67214, and therefore there is a concern that, depending on the reduction rate, the sharpness will deteriorate greatly and that a large amount of aliasing will appear. Particularly, in the case in which reduction is performed at a magnification approximating equal magnification, if a filter with a narrow pixel reference range is used the desired bandwidth limiting cannot be performed due to limitations of the filter characteristics, and the sharpness of the reduced image signal deteriorates. For example, there are cases in which aliasing appears.
In contrast, it is also conceivable to perform bandwidth limiting using a filter with a wide pixel reference range. However, if such a filter is mounted to a circuit, the memory capacity for holding pixel signal values used by the filter increases, and the scale of the circuit increases.